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| Gasconade Dolomite | |
|---|---|
| Name | Gasconade Dolomite |
| Type | Formation |
| Period | Ordovician |
| Lithology | Dolomite, chert, minor sandstone |
| Namedfor | Gasconade River |
| Namedby | Charles K. Swallow |
| Region | Missouri, United States |
| Country | United States |
| Underlies | Roubidoux Formation |
| Overlies | Eminence Dolomite |
Gasconade Dolomite is an Ordovician carbonate formation notable for its thick dolomitized sequences, chert nodules, and diverse fossil assemblages. It crops out extensively in the Ozark Plateau and has been central to studies in stratigraphy, paleontology, and regional economic geology. Research on the unit has involved state surveys, university departments, and national organizations documenting its lithofacies and biostratigraphic markers.
The unit consists predominantly of crystalline dolomite with interbedded chert, minor siliciclastic lenses, and locally peloidal textures; mapping and petrographic work have linked its fabric to dolomitization processes documented by researchers at Missouri Geological Survey, University of Missouri, and United States Geological Survey. Field descriptions emphasize bedded to massive dolomite, vuggy porosity, and stylolitic surfaces recognized in mapping projects by the National Park Service and state geologists. Petrographic thin-section studies performed by teams affiliated with U.S. Bureau of Mines, Iowa Geological Survey, and U.S. Geological Survey include descriptions of saddle dolomite, microcrystalline matrix, and secondary calcite cement. Regional hydrogeologic investigations by U.S. Environmental Protection Agency, Missouri Department of Natural Resources, and academic groups at Washington University in St. Louis treat porosity and permeability variations within the unit.
The formation is assigned to the Lower to Middle Ordovician based on conodont, trilobite, and brachiopod evidence analyzed by researchers at Smithsonian Institution, Harvard University, and Yale University. It conformably overlies the Eminence Dolomite in many sections mapped by the Geological Society of America and underlies the Roubidoux Formation in depositional frameworks used by the American Association of Petroleum Geologists and regional stratigraphers. Correlation with coeval units in the Appalachian Basin, Illinois Basin, and Canadian Shield has been proposed in comparative studies involving the Ohio Geological Survey, Indiana Geological Survey, and Ontario Geological Survey. Chronostratigraphic placement relies on biostratigraphic zones recognized by workers at Field Museum of Natural History and codified in monographs from the Paleontological Society.
Prominent exposures occur across the Ozark Plateau within Pulaski County, Missouri, Phelps County, Missouri, and Texas County, Missouri with measurable sections at classic localities near the Gasconade River, Springfield Plateau, and along roadcuts adjacent to Interstate 44. Outcrop belts have been cataloged by the Missouri Department of Natural Resources, St. Louis University, and regional field guides produced by the Missouri Geological Survey. Quarry exposures worked by contractors linked to U.S. Army Corps of Engineers projects and private aggregates operations provide additional sections used by researchers from University of Kansas and Missouri State University. Type sections and measured stratigraphic columns are deposited in repositories at the Missouri Geological Survey and collections at the University of Missouri Museum of Comparative Zoology.
Interpretations favor a shallow, epicontinental carbonate shelf setting influenced by tidal and shoal dynamics, an environment analogous to models developed by researchers at Scripps Institution of Oceanography, Woods Hole Oceanographic Institution, and the Lamont–Doherty Earth Observatory. Sedimentological evidence, including oolitic textures and cross-lamination, has been compared with modern analogs studied by teams from University of Miami, Florida State University, and Texas A&M University. Paleoecologic reconstructions of benthic assemblages reference comparative work at the Smithsonian Institution and faunal analogs cataloged in databases maintained by the Natural History Museum, London and the American Museum of Natural History. Geochemical proxies analyzed in laboratories at Ohio State University and Pennsylvania State University have been used to infer seawater chemistry and diagenetic histories.
Fossils include trilobites, brachiopods, gastropods, cephalopods, stromatolites, and microbial mats, documented in faunal accounts compiled by the Paleontological Society, University of Chicago, and the Field Museum. Trilobite taxa and brachiopod assemblages have been used for regional biostratigraphic correlations following schemes advanced by researchers at Harvard University and Yale University. Conodont elements recovered from phosphatic nodules have been investigated by paleontologists at Smithsonian Institution and U.S. Geological Survey laboratories to refine age assignments. Ichnofossils and trace-fossil suites have been described in reports from Purdue University and the University of Illinois Urbana–Champaign providing insight into benthic behavior and substrate conditions.
The unit serves as a source of crushed stone, dimension stone, and aggregate for construction projects overseen by Missouri Department of Transportation and private contractors; quarries supplying material have been documented by the Missouri Geological Survey and industry groups such as the National Stone, Sand & Gravel Association. Its porosity and fracture networks are of interest for groundwater resources assessed by the U.S. Geological Survey and Missouri Department of Natural Resources, and historic investigations into mineral occurrences have involved the U.S. Bureau of Mines and state mineral resource programs. Regional energy and subsurface storage studies by the National Energy Technology Laboratory and Department of Energy have occasionally evaluated dolomite units for reservoir potential.
The formation was named in early geological surveys of the Ozarks and appears in classical reports by surveyors associated with the Missouri Geological Survey, with historical treatments archived at the Library of Congress and referenced in publications of the Geological Society of America. Early mapping and stratigraphic frameworks were advanced by geologists affiliated with Washington University in St. Louis and later refined by stratigraphers at University of Missouri and federal programs in the U.S. Geological Survey. Specimen collections and type descriptions are curated in institutional collections at the University of Missouri Museum of Comparative Zoology, Field Museum of Natural History, and repositories maintained by the Missouri Department of Natural Resources.
Category:Ordovician geology of Missouri